The roar of earthquakes can be detected in orbit

GOCE satellite in the representation of the artist (image European Space Agency).

February 26, 2013. Last year, in the small town of Wisconsin (USA), there was a strange "boom." As it turned out, it was a small earthquake. And like this are not uncommon. In the early summer of 2001 residents Spokane (Washington) reported a similar noise, which lasted intermittently for about five months. Seismometers recorded then 105 aftershocks, the two — with a magnitude of 4.0. Some of them do not fall into the coverage area of seismographic equipment, so they were not able to locate. Installation of additional sensors indicated: land in July shook directly under the city.

And it is an occasion to reflect. In 2011, an earthquake in Christchurch (New Zealand), a magnitude of 6.3 has resulted in massive damage because the epicenter was located very close to the city. In 2009, L'Aquila, Italy by a series of small aftershocks followed the earthquake of the same magnitude (6.3), killing hundreds of people (and sent to prison six seismologists). It is therefore very important to know, thabout it occurs under Spokane. A group of researchers from the U.S. Geological Survey and the seismographic network Pacific Northwest has decided to seek help from satellites.

Data interferometric synthetic aperture radar can detect very small changes in the height of the earth's surface, which, in particular, causes displacement of blocks of the earth's crust during earthquakes. The information collected by the satellites of the European and Canadian space agencies to suggest the movement along the fault to the north-east of the city center. Despite the fact that the ground viewed from space to register a shift of about 15 mm.

Computer simulations show that the observations correspond to a shallow earthquake with an epicenter just 0.3-2 km below the surface. One block pushes up another and that are moved by 45 mm.

Signs of fracture outside the city are not convincing. Flood waters from the ancient glacial lake Missoula erased all traces of it. Fault, however, there is on the other side of the city, and perhaps they are offshoots of each other.

Seismologists have to know more about the structure of the fault and that is why he is restless. If you do not know the pressure in the fault, you will not be able to assess the strength of a possible earthquake.

As for the noise, it is inherent not only easy jolts. In 2011 the Japanese earthquake Tohoku-Oki 9.0 magnitude sounded too — so much so that the noise recorded at a height of 270 km.

European satellite GOCE created for other purposes. In fact, it's a giant accelerometer capable of incredibly accurate measurement of the force of gravity. It is commonly used to study processes such as ocean circulation and the melting of the ice sheets. But a group of scientists from France and the Netherlands decided to find every single satellite data associated with the earthquake in Japan. And she's not looking for information about changes to the Earth's surface, and information about the infrasonic signal, which reached satellites.

See also: Planet Ocean Model

Indeed, the GOCE accelerometer reacted to a weak effect of acoustic wave transmitted through it. Moreover, since the satellite's orbit, strictly speaking, is within the atmosphere, it could detect fluctuations in air density caused by the passage of sound waves. Reading accuracy of the probe depends on the exposure to a well-defined height with a given density of air, and these fluctuations have led to the launch of engines: Automatic decided that the satellite had lost his orbit.

Therefore GOCE can claim to be the first orbital seismometer. He revealed that another possible way of studying atmospheric phenomena associated with earthquakes — such as disturbances in the ionosphere that can interfere with the system GPS.

The results were published in the Journal of Geophysical Research — Solid Earth and Geophysical Research Letters.

Based on: Ars Technica
Source: Kompyulenta

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